1. Field of the Invention
The present invention relates to a semiconductor light receiving device including a light receiving region formed on a semiconductor substrate and an electrode formed in a peripheral portion of the light receiving region on the semiconductor substrate in order to transfer a charge that has been generated through photoelectric conversion in the light receiving region to the outside of the light receiving region, and to a manufacturing method for the same. In particular, the present invention relates to a technique for improving the efficiency of light convergence to the light receiving region.
2. Description of the Related Art
Conventional semiconductor light receiving devices such as a CCD type image pickup device or a MOS type image pickup device are disclosed, for example, in JP-A2002-164522 or in JP-A2001-77339. FIG. 3 is a cross sectional view showing an example of a conventional semiconductor light receiving device.
As shown in FIG. 3, a semiconductor light receiving device has a structure in that an n-type vertical resistor 2, a p+-type channel stopper 3, an n-type light receiving region 4, a p++-type hole accumulating region 5 formed in a surface of the light receiving region 4, and a read-out gate 6 existing between the light receiving region 4 and the vertical resistor 2 are formed in a semiconductor substrate 1 (or a p-type well 1 formed in a surface of a semiconductor substrate). Further, a gate insulating film 7, a transfer electrode 8 made of polycrystal silicon, an interlayer insulating film 9 made of SiO2 obtained by thermally oxidizing, for example, polycrystal silicon, a light blocking film 10 made of, for example, aluminum (Al) or tungsten (W), an aperture 11 which is a light receiving window formed by etching and removing a portion of the light blocking film 10 that corresponds to each light receiving region 4, a passivation film 12 formed on the light blocking film 10, a planar film 13 made of resin formed on the passivation film 12, a color filter layer 14 and an on-chip lens 15 are formed on the surface of the semiconductor substrate 1.
Here, the gate insulating film 7 may be, for example, a single layered film of SiO2 (MOS structure) or a three layered film of SiO2/SiN/SiO2 (MONOS structure). Further, the transfer electrode 8 may be made of the first polycrystal silicon layer or may be made of the second polycrystal silicon layer. FIG. 3 only illustrates the transfer electrode 8 made of one of the first and second polycrystal silicon layers.
Demand for an increase in the number of pixels and for miniaturization is strong for semiconductor light receiving devices such as a solid-state image pickup device and miniaturization of each pixel has been progressing. Accordingly, the amount of light convergence into the light receiving region in each pixel tends to decrease and, corresponding with this, problems such as lowering of sensitivity, deterioration of smear characteristics, increase in dark current and increase in the number of image defects arise. Thus, a decrease in the amount of light convergence due to miniaturization of pixels cannot be avoided to a certain extent, while reflection of a part of light to be incident to the light receiving region 4 caused by the difference in indexes of refraction between silicon Si and silicon oxide SiO2 at the border between the semiconductor substrate (or well) 1 made of silicon Si and the gate insulating film 7 made of, for example, silicon oxide SiO2 formed on the semiconductor substrate 1 can be cited as one factor of the lowering of sensitivity.
In addition, an increase in dark current and an increase in the number of image defects are caused by dangling bonds generated in the vicinity of the surface of the semiconductor substrate 1 where the supply of hydrogen atoms paired with dangling bonds for stabilization becomes insufficient. Furthermore, the surface of the light blocking film 10 made of, for example, aluminum Al is covered with the passivation film 12 made of a glass-based insulator and problems arise where reflections often occur on the surface of the light blocking film 10, so that satin irregularity and flare, which are spurious signals, occur due to those reflections.
In order to cope with these problems, reduction of noise has been found in JP-A 2002-164522 by forming a silicon nitride film after the formation of the aperture 11. In order to further progress in miniaturization, however, a further improvement in the efficiency of light convergence is required. In addition, anisotropic etching (reactive ion etching) suitable for miniaturization has been used in the pattern formation of electrodes in the above-described conventional techniques wherein the electrodes are in the form where the sidewalls are approximately perpendicular to the surface of the substrate.